In a related-art image forming apparatus such a color printer, a tandem-type image forming apparatus includes photosensitive drums disposed in parallel for colors of yellow, magenta, cyan and black.
In the tandem-type image forming apparatus, developing rollers are provided for photosensitive drums, respectively. By rotating the photosensitive drums and the developing rollers in such a state that the developing rollers are in contact with the photosensitive drums, toner is supplied from the developing rollers to form electrostatic latent images on the photosensitive drums, whereby toner images are carried on the photosensitive drums. A color image forming is performed on a sheet by forming color toner images on the photosensitive drums, respectively, and transferring the color toner images of the respective colors onto the sheet in an overlapping manner. A monochrome image forming is performed on a sheet by forming a black toner image only on the photosensitive drum for black, and transferring the black toner image onto the sheet.
As such a tandem-type image forming apparatus, JP-A-2007-178654 describes an image forming apparatus which includes a translation cam member which is movable along a straight line in a direction in which photosensitive drums are arranged. The translation cam member is provided for switching a state among a total separated state in which all the developing rollers are separated from the photosensitive drums, a black contact state in which the developing roller contacts the photosensitive drum for black while the other developing rollers are separated from the photosensitive drums for yellow, magenta and cyan, and a total contact state in which all the developing rollers contact all the photosensitive drums, respectively.
Additionally, in an image forming apparatus, each of developing cartridges which hold developing rollers is provided with a memory chip for storing information related to the developing cartridge.